Vibrational spectra, NBO, HOMO-LUMO and conformational stability studies of 4-hydroxythiobenzamide.

In this work, the experimental and theoretical study on molecular structure, vibrational spectral analysis of 4-hydroxythiobenzamide (HTB) have been reported. The solid phase FTIR (4000-400 cm(-1)) and FT-Raman spectra (3500-50 cm(-1)) were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of HTB in the ground-state have been calculated by the density functional method (B3LYP) with 6-311+G(d,p) and 6-311++G(d,p) as basis sets. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Stability of the molecule arising from hyperconjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that the value of electron density (ED) in the σ(∗) antibonding orbitals and E((2)) energies confirms the occurrence of ICT (intra-molecular charge transfer) within the molecule. The UV spectrum was measured in ethanol solution. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) correlates with the experimental findings. The calculated molecular electrostatic potential (MESP), HOMO and LUMO energies show that charge transfer occurs within the molecule. Besides, the simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.